The news comes after protesters circulated a map which identifies more than 125 targets across the City, including dozens of international corporations, banks, and oil companies.

More than 50 financial institutions are pinpointed, including some of those – like Royal Bank of Scotland, Lloyds TSB – blamed for precipitating the current economic crisis.

The map urged potential demonstrators to vent their anger at the “carpeted, warmed and well-lighted offices” of corporate capitalism, quoting the writer CS Lewis’s attack on the “managerial age”.

None of the main banks would comment. However senior banking figures told telegraph.co.uk that they were taking the security threat seriously, and admitted that they were concerned about the possibility of trouble.

Frankly, these summits have increasingly brought out more and more crazies through the years. I don’t blame them for wanting to stay clear of these protesters.